﻿using System;
using System.IO;
using System.Text;

public sealed class MD5 : IDisposable
{
    #region ------------------ IDisposable Members ------------------

    public void Dispose()
    {
        Dispose(true);
    }

    #endregion

    #region ------------------ Instance Methods ------------------

    private void Dispose(bool disposing)
    {
        if (!disposing)
            Initialize();
    }

    #endregion

    #region ------------------ Static Methods ------------------

    public static MD5 Create(string hashName)
    {
        if (hashName == "MD5")
            return new MD5();
        throw new NotSupportedException();
    }

    public static string GetMd5String(string source)
    {
        var md = Create();
        byte[] hash;
        //Create a new instance of ASCIIEncoding to
        //convert the string into an array of Unicode bytes.
        var enc = new UTF8Encoding();
        //            ASCIIEncoding enc = new ASCIIEncoding();
        //Convert the string into an array of bytes.
        var buffer = enc.GetBytes(source);
        //Create the hash value from the array of bytes.
        hash = md.ComputeHash(buffer);
        var sb = new StringBuilder();
        foreach (var b in hash)
            sb.Append(b.ToString("x2"));
        return sb.ToString();
    }

    public static MD5 Create()
    {
        return new MD5();
    }

    #endregion

    #region base implementation of the MD5

    #region constants

    private const byte S11 = 7;
    private const byte S12 = 12;
    private const byte S13 = 17;
    private const byte S14 = 22;
    private const byte S21 = 5;
    private const byte S22 = 9;
    private const byte S23 = 14;
    private const byte S24 = 20;
    private const byte S31 = 4;
    private const byte S32 = 11;
    private const byte S33 = 16;
    private const byte S34 = 23;
    private const byte S41 = 6;
    private const byte S42 = 10;
    private const byte S43 = 15;
    private const byte S44 = 21;

    private static readonly byte[] PADDING = new byte[]
                                                     {
                                                         0x80, 0, 0, 0, 0, 0,
                                                         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                                                         0, 0, 0, 0, 0, 0, 0,
                                                         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
                                                         0, 0, 0, 0, 0, 0, 0,
                                                         0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
                                                     };

    #endregion

    #region F, G, H and I are basic MD5 functions.

    private static uint F(uint x, uint y, uint z)
    {
        return (((x) & (y)) | ((~x) & (z)));
    }

    private static uint G(uint x, uint y, uint z)
    {
        return (((x) & (z)) | ((y) & (~z)));
    }

    private static uint H(uint x, uint y, uint z)
    {
        return ((x) ^ (y) ^ (z));
    }

    private static uint I(uint x, uint y, uint z)
    {
        return ((y) ^ ((x) | (~z)));
    }

    #endregion

    #region rotates x left n bits.

    /// <summary>
    ///   rotates x left n bits.
    /// </summary>
    /// <param name = "x"></param>
    /// <param name = "n"></param>
    /// <returns></returns>
    private static uint ROTATE_LEFT(uint x, byte n)
    {
        return (((x) << (n)) | ((x) >> (32 - (n))));
    }

    #endregion

    #region FF, GG, HH, and II transformations

    /// FF, GG, HH, and II transformations
    /// for rounds 1, 2, 3, and 4.
    /// Rotation is separate from addition to prevent recomputation.
    private static void FF(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
    {
        (a) += F((b), (c), (d)) + (x) + (ac);
        (a) = ROTATE_LEFT((a), (s));
        (a) += (b);
    }

    private static void GG(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
    {
        (a) += G((b), (c), (d)) + (x) + (ac);
        (a) = ROTATE_LEFT((a), (s));
        (a) += (b);
    }

    private static void HH(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
    {
        (a) += H((b), (c), (d)) + (x) + (ac);
        (a) = ROTATE_LEFT((a), (s));
        (a) += (b);
    }

    private static void II(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
    {
        (a) += I((b), (c), (d)) + (x) + (ac);
        (a) = ROTATE_LEFT((a), (s));
        (a) += (b);
    }

    #endregion

    #region context info

    /// <summary>
    ///   state (ABCD)
    /// </summary>
    private readonly uint[] state = new uint[4];

    /// <summary>
    ///   number of bits, modulo 2^64 (lsb first)
    /// </summary>
    private readonly uint[] count = new uint[2];

    /// <summary>
    ///   input buffer
    /// </summary>
    private readonly byte[] buffer = new byte[64];

    #endregion

    #region ------------------ Constructors ------------------

    internal MD5()
    {
        Initialize();
    }

    #endregion

    #region ------------------ Instance Methods ------------------

    /// <summary>
    ///   MD5 initialization. Begins an MD5 operation, writing a new context.
    /// </summary>
    /// <remarks>
    ///   The RFC named it "MD5Init"
    /// </remarks>
    public void Initialize()
    {
        count[0] = count[1] = 0;
        // Load magic initialization constants.
        state[0] = 0x67452301;
        state[1] = 0xefcdab89;
        state[2] = 0x98badcfe;
        state[3] = 0x10325476;
    }

    /// <summary>
    ///   MD5 block update operation. Continues an MD5 message-digest
    ///   operation, processing another message block, and updating the
    ///   context.
    /// </summary>
    /// <param name = "input"></param>
    /// <param name = "offset"></param>
    /// <param name = "count"></param>
    /// <remarks>
    ///   The RFC Named it MD5Update
    /// </remarks>
    private void HashCore(byte[] input, int offset, int count)
    {
        int i;
        int index;
        int partLen;
        // Compute number of bytes mod 64
        index = (int)((this.count[0] >> 3) & 0x3F);
        // Update number of bits
        if ((this.count[0] += ((uint)count << 3)) < ((uint)count << 3))
            this.count[1]++;
        this.count[1] += ((uint)count >> 29);
        partLen = 64 - index;
        // Transform as many times as possible.
        if (count >= partLen)
        {
            Buffer.BlockCopy(input, offset, buffer, index, partLen);
            Transform(buffer, 0);
            for (i = partLen; i + 63 < count; i += 64)
                Transform(input, offset + i);
            index = 0;
        }
        else
            i = 0;
        // Buffer remaining input
        Buffer.BlockCopy(input, offset + i, buffer, index, count - i);
    }

    /// <summary>
    ///   MD5 finalization. Ends an MD5 message-digest operation, writing the
    ///   the message digest and zeroizing the context.
    /// </summary>
    /// <returns>message digest</returns>
    /// <remarks>
    ///   The RFC named it MD5Final
    /// </remarks>
    private byte[] HashFinal()
    {
        var digest = new byte[16];
        var bits = new byte[8];
        int index, padLen;
        // Save number of bits
        Encode(bits, 0, count, 0, 8);
        // Pad out to 56 mod 64.
        index = (int)((count[0] >> 3) & 0x3f);
        padLen = (index < 56) ? (56 - index) : (120 - index);
        HashCore(PADDING, 0, padLen);
        // Append length (before padding)
        HashCore(bits, 0, 8);
        // Store state in digest
        Encode(digest, 0, state, 0, 16);
        // Zeroize sensitive information.
        count[0] = count[1] = 0;
        state[0] = 0;
        state[1] = 0;
        state[2] = 0;
        state[3] = 0;
        // initialize again, to be ready to use
        Initialize();
        return digest;
    }

    /// <summary>
    ///   MD5 basic transformation. Transforms state based on 64 bytes block.
    /// </summary>
    /// <param name = "block"></param>
    /// <param name = "offset"></param>
    private void Transform(byte[] block, int offset)
    {
        uint a = state[0], b = state[1], c = state[2], d = state[3];
        var x = new uint[16];
        Decode(x, 0, block, offset, 64);
        // Round 1
        FF(ref a, b, c, d, x[0], S11, 0xd76aa478); /* 1 */
        FF(ref d, a, b, c, x[1], S12, 0xe8c7b756); /* 2 */
        FF(ref c, d, a, b, x[2], S13, 0x242070db); /* 3 */
        FF(ref b, c, d, a, x[3], S14, 0xc1bdceee); /* 4 */
        FF(ref a, b, c, d, x[4], S11, 0xf57c0faf); /* 5 */
        FF(ref d, a, b, c, x[5], S12, 0x4787c62a); /* 6 */
        FF(ref c, d, a, b, x[6], S13, 0xa8304613); /* 7 */
        FF(ref b, c, d, a, x[7], S14, 0xfd469501); /* 8 */
        FF(ref a, b, c, d, x[8], S11, 0x698098d8); /* 9 */
        FF(ref d, a, b, c, x[9], S12, 0x8b44f7af); /* 10 */
        FF(ref c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
        FF(ref b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
        FF(ref a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
        FF(ref d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
        FF(ref c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
        FF(ref b, c, d, a, x[15], S14, 0x49b40821); /* 16 */
        // Round 2
        GG(ref a, b, c, d, x[1], S21, 0xf61e2562); /* 17 */
        GG(ref d, a, b, c, x[6], S22, 0xc040b340); /* 18 */
        GG(ref c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
        GG(ref b, c, d, a, x[0], S24, 0xe9b6c7aa); /* 20 */
        GG(ref a, b, c, d, x[5], S21, 0xd62f105d); /* 21 */
        GG(ref d, a, b, c, x[10], S22, 0x2441453); /* 22 */
        GG(ref c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
        GG(ref b, c, d, a, x[4], S24, 0xe7d3fbc8); /* 24 */
        GG(ref a, b, c, d, x[9], S21, 0x21e1cde6); /* 25 */
        GG(ref d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
        GG(ref c, d, a, b, x[3], S23, 0xf4d50d87); /* 27 */
        GG(ref b, c, d, a, x[8], S24, 0x455a14ed); /* 28 */
        GG(ref a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
        GG(ref d, a, b, c, x[2], S22, 0xfcefa3f8); /* 30 */
        GG(ref c, d, a, b, x[7], S23, 0x676f02d9); /* 31 */
        GG(ref b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */
        // Round 3
        HH(ref a, b, c, d, x[5], S31, 0xfffa3942); /* 33 */
        HH(ref d, a, b, c, x[8], S32, 0x8771f681); /* 34 */
        HH(ref c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
        HH(ref b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
        HH(ref a, b, c, d, x[1], S31, 0xa4beea44); /* 37 */
        HH(ref d, a, b, c, x[4], S32, 0x4bdecfa9); /* 38 */
        HH(ref c, d, a, b, x[7], S33, 0xf6bb4b60); /* 39 */
        HH(ref b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
        HH(ref a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
        HH(ref d, a, b, c, x[0], S32, 0xeaa127fa); /* 42 */
        HH(ref c, d, a, b, x[3], S33, 0xd4ef3085); /* 43 */
        HH(ref b, c, d, a, x[6], S34, 0x4881d05); /* 44 */
        HH(ref a, b, c, d, x[9], S31, 0xd9d4d039); /* 45 */
        HH(ref d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
        HH(ref c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
        HH(ref b, c, d, a, x[2], S34, 0xc4ac5665); /* 48 */
        // Round 4
        II(ref a, b, c, d, x[0], S41, 0xf4292244); /* 49 */
        II(ref d, a, b, c, x[7], S42, 0x432aff97); /* 50 */
        II(ref c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
        II(ref b, c, d, a, x[5], S44, 0xfc93a039); /* 52 */
        II(ref a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
        II(ref d, a, b, c, x[3], S42, 0x8f0ccc92); /* 54 */
        II(ref c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
        II(ref b, c, d, a, x[1], S44, 0x85845dd1); /* 56 */
        II(ref a, b, c, d, x[8], S41, 0x6fa87e4f); /* 57 */
        II(ref d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
        II(ref c, d, a, b, x[6], S43, 0xa3014314); /* 59 */
        II(ref b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
        II(ref a, b, c, d, x[4], S41, 0xf7537e82); /* 61 */
        II(ref d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
        II(ref c, d, a, b, x[2], S43, 0x2ad7d2bb); /* 63 */
        II(ref b, c, d, a, x[9], S44, 0xeb86d391); /* 64 */
        state[0] += a;
        state[1] += b;
        state[2] += c;
        state[3] += d;
        // Zeroize sensitive information.
        for (var i = 0; i < x.Length; i++)
            x[i] = 0;
    }

    #endregion

    #region ------------------ Static Methods ------------------

    /// <summary>
    ///   Encodes input (uint) into output (byte). Assumes len is
    ///   multiple of 4.
    /// </summary>
    /// <param name = "output"></param>
    /// <param name = "outputOffset"></param>
    /// <param name = "input"></param>
    /// <param name = "inputOffset"></param>
    /// <param name = "count"></param>
    private static void Encode(byte[] output, int outputOffset, uint[] input, int inputOffset, int count)
    {
        int i, j;
        var end = outputOffset + count;
        for (i = inputOffset, j = outputOffset; j < end; i++, j += 4)
        {
            output[j] = (byte)(input[i] & 0xff);
            output[j + 1] = (byte)((input[i] >> 8) & 0xff);
            output[j + 2] = (byte)((input[i] >> 16) & 0xff);
            output[j + 3] = (byte)((input[i] >> 24) & 0xff);
        }
    }

    /// <summary>
    ///   Decodes input (byte) into output (uint). Assumes len is
    ///   a multiple of 4.
    /// </summary>
    /// <param name = "output"></param>
    /// <param name = "outputOffset"></param>
    /// <param name = "input"></param>
    /// <param name = "inputOffset"></param>
    /// <param name = "count"></param>
    private static void Decode(uint[] output, int outputOffset, byte[] input, int inputOffset, int count)
    {
        int i, j;
        var end = inputOffset + count;
        for (i = outputOffset, j = inputOffset; j < end; i++, j += 4)
            output[i] = (input[j]) | (((uint)input[j + 1]) << 8) | (((uint)input[j + 2]) << 16) |
                        (((uint)input[j + 3]) <<
                         24);
    }

    #endregion

    #endregion

    #region expose the same interface as the regular MD5 object

    #region ------------------ Instance Methods ------------------

    public void Clear()
    {
        Dispose(true);
    }

    public byte[] ComputeHash(byte[] buffer)
    {
        return ComputeHash(buffer, 0, buffer.Length);
    }

    public byte[] ComputeHash(byte[] buffer, int offset, int count)
    {
        Initialize();
        HashCore(buffer, offset, count);
        HashValue = HashFinal();
        return (byte[])HashValue.Clone();
    }

    public byte[] ComputeHash(Stream inputStream)
    {
        Initialize();
        var count = 0;
        var buffer = new byte[4096];
        while (0 < (count = inputStream.Read(buffer, 0, 4096)))
        {
            HashCore(buffer, 0, count);
        }
        HashValue = HashFinal();
        return (byte[])HashValue.Clone();
    }

    public int TransformBlock(
        byte[] inputBuffer,
        int inputOffset,
        int inputCount,
        byte[] outputBuffer,
        int outputOffset
        )
    {
        if (inputBuffer == null)
        {
            throw new ArgumentNullException("inputBuffer");
        }
        if (inputOffset < 0)
        {
            throw new ArgumentOutOfRangeException("inputOffset");
        }
        if ((inputCount < 0) || (inputCount > inputBuffer.Length))
        {
            throw new ArgumentException("inputCount");
        }
        if ((inputBuffer.Length - inputCount) < inputOffset)
        {
            throw new ArgumentOutOfRangeException("inputOffset");
        }
        if (State == 0)
        {
            Initialize();
            State = 1;
        }
        HashCore(inputBuffer, inputOffset, inputCount);
        if ((inputBuffer != outputBuffer) || (inputOffset != outputOffset))
        {
            Buffer.BlockCopy(inputBuffer, inputOffset, outputBuffer, outputOffset, inputCount);
        }
        return inputCount;
    }

    public byte[] TransformFinalBlock(
        byte[] inputBuffer,
        int inputOffset,
        int inputCount
        )
    {
        if (inputBuffer == null)
        {
            throw new ArgumentNullException("inputBuffer");
        }
        if (inputOffset < 0)
        {
            throw new ArgumentOutOfRangeException("inputOffset");
        }
        if ((inputCount < 0) || (inputCount > inputBuffer.Length))
        {
            throw new ArgumentException("inputCount");
        }
        if ((inputBuffer.Length - inputCount) < inputOffset)
        {
            throw new ArgumentOutOfRangeException("inputOffset");
        }
        if (State == 0)
        {
            Initialize();
        }
        HashCore(inputBuffer, inputOffset, inputCount);
        HashValue = HashFinal();
        var buffer = new byte[inputCount];
        Buffer.BlockCopy(inputBuffer, inputOffset, buffer, 0, inputCount);
        State = 0;
        return buffer;
    }

    #endregion

    #region ------------------ Properties ------------------

    public bool CanReuseTransform
    {
        get { return true; }
    }

    public bool CanTransformMultipleBlocks
    {
        get { return true; }
    }

    public byte[] Hash
    {
        get
        {
            if (State != 0)
                throw new InvalidOperationException();
            return (byte[])HashValue.Clone();
        }
    }

    public int HashSize
    {
        get { return HashSizeValue; }
    }

    public int InputBlockSize
    {
        get { return 1; }
    }

    public int OutputBlockSize
    {
        get { return 1; }
    }

    #endregion

    #region ------------------ Instance Fields ------------------

    private byte[] HashValue;
    private int State;
    private int HashSizeValue = 128;

    #endregion

    #endregion
}
